A bench test evaluation of a neonatal closed tracheal suction system

We tested the hypothesis that a possible mechanism for reduced hypoxia during suctioning with closed tracheal suction systems (CTSS) is the provision of uninterrupted gas delivery and the maintenance of airway pressures. This was accomplished by using a neonatal ventilator and test lung model to permit the insertion of a CTSS (with and without suction applied), measurements of inspiratory and end-expiratory airway pressures proximal and distal to the endotracheal tube (ETT) and measurements of inspired and expired tidal volumes (sampled distal to the ETT). An 8 Fr CTSS was evaluated with 4.5, 4.0, and 3.5 mm ETT, and a 6 Fr CTSS with a 3.5, 3.0, and 2.5 mm ETT. We found that catheter placement without suction caused no changes in proximal airway pressures but distal peak inspiratory pressures decreased as the relationship between suction catheter size and ETT lumen increased, while distal end-expiratory pressures were unchanged. Similarly, distal tidal volumes progressively decreased as the size of the suction catheter occupied more of the ETT lumen. During suctioning with the 6 Fr catheter, proximal airway pressures were virtually unchanged; however, as ETT size decreased, distal airway pressures also decreased. The application of suction only modestly augmented the substantial decrement in measured tidal volumes when compared to catheter insertion alone. For the 8 Fr catheter, suction markedly reduced both proximal and distal airway pressures and tidal volumes. We conclude that the use of the CTSS tested in this neonatal ventilator/test lung model does not preserve continuity of volume or pressure delivery during suction procedures; therefore these cannot be the sole explanation for the reported reduction in suction related hypoxia.